Silicon carbide (SiC) and silicon nitride (Si.sub.3 N.sub.4) solids are covalent compounds. They resist fusion or consolidation via ordinarily used methods such as sintering and even hot pressing. In order to prepare sound solids from SiC and Si.sub.3 N.sub.4 powders, it is therefore necessary to add sintering aids such as magnesia (MgO), or yttria and alumina. Of these, magnesia is the most preferred additive in certain cases such as high temperature bearings. References attesting to this need for additives are available.
In recent years, the demands on metallic materials' performance has increased substantially. For example, turbine blades and bearings are increasingly subjected to higher operating temperatures. Thus, while jet engine components operate at .about.1800.degree. F., there is a great need for raising the operating temperatures to as high as 2400.degree. F. No known metallic material, be it steel, cobalt, or a nickel base alloy, meets the requirements for operation at, say, 2000 to 2200.degree. F. for long periods of time. If jet engines can be operated at these temperatures, considerable gains in performance can be attained. Ceramics such as SiC, Si.sub.3 N.sub.4 and combinations of the two are considered as potential replacements of metallic alloy. This invention is concerned with "new" approach(es) capable of yielding dense Si.sub.3 N.sub.4 and SiC composite materials of high strength and high fracture toughness. In particular, the method affords a novel technique for fabricating SiC whisker reinforced ceramics.
U.S. Pat. No. 4,134,759 to Yajima discloses the coating of long SiC fibers with liquid molten magnesium. The coating of short fibers or whiskers made of SiC presents a different problem than the one confronting Yajima.
In the Yajima patent the long fibers of SiC are pulled or advanced through a bath of molten Mg. The Yajima method could therefore, not be applied to the coating of very short fibrous materials.